"Our office will spare no resource, and will work with professionalism, integrity and diligence, in a way that honors the memories of the victims."
Bowers remained in custody ahead of a preliminary hearing scheduled for tomorrow.
Members of Pittsburgh's grief-stricken Jewish community, meanwhile, endured another round of funerals for the congregants who were gunned down. Melvin Wax, 87, Irving Younger, 69, and Joyce Fienberg, 75, were being laid to rest as part of a weeklong series of services.
The indictment charges Bowers with killing 11 people, and for each of those victims, he faces separate counts of obstruction of free exercise of religion resulting in death, and using a firearm to commit murder during a crime of violence.
He also faces charges of attempting to kill people exercising their religious beliefs, and civil rights charges related to injuring several police officers who responded to the attack.
The charges carry a possible death sentence, and the Justice Department has said previously that federal prosecutors in Pittsburgh had initiated the process to seek such a punishment. The case, though, must still be reviewed by Justice Department lawyers specialising in capital cases, and the final decision will ultimately be left to the Attorney-General.
Bowers also faces number of state charges filed over the weekend, including 11 counts of criminal homicide. Allegheny County District Attorney Stephen Zappala said yesterday that his office sought to have Bowers arraigned on the state charges but were denied by federal authorities.
Zappala said that he would prefer that local residents "sit in judgment" of Bowers in a trial, but instead would let the federal case proceed and put the state charges on hold for the time being.
Federal investigators concluded that Bowers legally acquired and possessed all of the guns recovered from Tree of Life synagogue and his home, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives.
Authorities have not said whether Bowers - who was wounded during the gun battle with police responding to the synagogue - is cooperating with investigators or detailed what he may have told them.
But according to the hospital that treated him for two days after the attack, he continued making comments there about wanting to kill Jews, even though some of the nurses and doctors who treated him were Jewish.
- additional reporting AP